In the field of orthopedics for treating diseases and injuries of the bone, joint, muscle, nerve, and the like, plain radiography is often used to observe the joint or the like with a still image.
Besides, X-ray fluoroscopy is also used to observe the joint or the like with a moving image for displaying it in real time using X-rays.
In addition, there is a case that a slice of a three-dimensional image captured of the joint or the like is reconstructed using a multi-planar reconstruction (MPR), and the MPR image is used to observe the joint or the like.
FIGS. 1A to 1E are diagrams illustrating examples of joint movements. For example, FIG. 1E illustrates the twisting movement of the wrist. A joint disorder is diagnosed by observing the movement of the bones and ligaments during such a joint movement. In the observation of the movement of the bones and ligaments, it is checked how a gap between a problematic bone and a bone adjacent thereto changes during the joint movement. Hereinafter, the bone may sometimes be referred to as “hard tissue”.
The dynamics of the joint cannot be observed with a still image. Incidentally, “the dynamics of the joint” refers to the positional change of two hard tissues of the joint, which are moving relative to each other, and changes in a gap between the hard tissues.
The dynamics of the joint can be observed with a moving image. However, when the two hard tissues of the joint are moving relative to each other, the hard tissues appear overlapped depending on the viewing direction. In this case, the positional change of the two hard tissues and changes in a gap between them cannot be observed appropriately. Therefore, it is difficult to observe the dynamics of the joint.
Besides, when the dynamics of the joint is observed with an MPR image, even if one of the hard tissues is fixed, the other may sometimes disappear from the MPR image. Accordingly, it is difficult to observe the dynamics of the joint.